(Annuity payments) Calvin Johnson has a $4,500 debt balance on his Visa card that charges 17.2 percent APR compounded monthly. In 2009, Calvin's minimum monthly payment is 4 percent of his debt balance, which is $180. How many months (round up) will it take Calvin Johnson to pay off his credit card if he pays the current minimum payment of $180 at the end of each month? In 2010, as the result of a federal mandate, the minimum monthly payment on credit cards rose to 5 percent. If Calvin made monthly payments of $225 at the end of each month, how long would it take to pay off his credit card